Contribution of Exogenous Proline to Abiotic Stresses Tolerance in Plants: A Review

Abstract

Abiotic stresses are the major environmental factors that play a significant role in decreasing plant yield and production potential by influencing physiological, biochemical, and molecular processes. Abiotic stresses and global population growth have prompted scientists to use beneficial strategies to ensure food security. The use of organic compounds to improve tolerance to abiotic stresses has been considered for many years. For example, the application of potential external osmotic protective compounds such as proline is one of the approaches to counteract the adverse effects of abiotic stresses on plants. Proline level increases in plants in response to environmental stress. Proline accumulation is not just a signal of tension. Rather, according to research discussed in this article, this biomolecule improves plant resistance to abiotic stress by rising photosynthesis, enzymatic and non-enzymatic antioxidant activity, regulating osmolyte concentration, and sodium and potassium homeostasis. In this review, we discuss the biosynthesis, sensing, signaling, and transport of proline and its role in the development of various plant tissues, including seeds, floral components, and vegetative tissues. Further, the impacts of exogenous proline utilization under various non-living stresses such as drought, salinity, high and low temperatures, and heavy metals have been extensively studied. Numerous various studies have shown that exogenous proline can improve plant growth, yield, and stress tolerance under adverse environmental factors.

Keywords: drought stress; exogenous application; foliar spray; osmoprotectants; salinity stress; seed priming.

Figure 1

The metabolic pathway of proline synthesis in plants through glutamate and ornithine. Orn (represents ornithine), OAT (ornithine aminotransferase), Glu (glutamic acid), P5CS (delta-1-pyrroline-5-carboxylate synthase), P5CDH (delta-1-pyrroline-5-carboxylate dehydrogenase), GSA (glutamate-1-semialdehyde), P5C (pyrroline-5-carboxylate), P5CR (pyrroline-5-carboxylate reductase), ProDH (proline dehydrogenase).

Figure 2

The summarized physiological and biochemical changes observed under the influence of exogenous proline that have beneficial effects on the tolerance of stress factors in cultivated plants. Up-regulated processes and/or biochemicals are marked in green, down-regulated are marked in red. For detailed information refer to text.